A novel model used to compare water-perfused and solid-state anorectal manometry

Background: Anal pressures are commonly measured using water-perfused and solid-state manometers. We constructed a dynamic model of the anus to compare the agreement and reproducibility of the two types of manometers. Methods: The model system was constructed using a pig anorectum together with an inflatable bowel sphincter. The pig anorectum was mounted on a jig and the sphincter was inserted external to the internal sphincter. The sphincter pressure was adjusted over the range 20 to 185 mmHg. At each of 24 constant sphincter pressures, triplicate readings were carried out with both manometers. The first measurement by each method was used for the comparison. The replicate measurements were used to calculate measures of repeatability for each method. Results: Measurements by the two manometers were highly correlated (r=0.97). Measurements by the solid state manometer were higher than the water-perfused manometer by 8.1±12.2 mmHg (mean±SD). Precision (coefficient of variation) for the solid-state manometer (2.8%) was better than for the water-perfused manometer (8.3%). Conclusions: The new model of the anal canal shows promise as a tool for assessing physiological interventions. The solid-state manometer has many advantages over the water-perfused manometer, providing more consistent measurements at clinically relevant pressures.